1. Technical Field
Embodiments relate to a three-dimensional integrated image sensor enabling to obtain information relative to the distance to objects contained in a scene. More specifically, the present invention relates to such a sensor capable of detecting objects at macroscopic distances.
2. Discussion of the Related Art
“Three-dimensional (3D) macroscopic image sensor” here designates image sensors that allow measurement of the remoteness of objects located at distances greater than approximately one centimeter.
Many techniques for acquiring three-dimensional images and obtaining information as to the distance to objects are known. Among these, stereo vision techniques provide, to obtain a 3D rendering of an image, performing two acquisitions of a same scene by means of two cameras placed at distant points. The two images acquired by the two cameras are then modified by being applied, for example, to a color filter, and then combined. For the reading of the image, two color filters, each capable of filtering one of the two initial images, are placed before a person's eyes. The human brain combines the two images seen by the person's two eyes and reconstructs the initial three-dimensional image.
Using this technique to perform an automated mapping of the distance to objects contained in a scene (stereoscopic method) is relatively complex. Indeed, to perform such a mapping, the two cameras should be perfectly aligned with the objects contained in the scene, and a system for decoding the complex data should be used to obtain information as to the remoteness of the objects. It is thus difficult to manufacture mobile devices using this method.
Another method for determining the distance to an object is known as the TOF method (“Time of Flight”). This method, especially used in aeronautics, comprises sending a wave, for example, a light or acoustic wave, towards an object and calculating the time taken by the wave to travel to the object and back. This method is however not adapted to the measurement of short distances. Indeed, in this case, the time taken by the wave to travel to the object and back is too short to be easily detected by a sensor and does not enable to accurately determine close distances. Further, this method is not compatible with the performing of an instantaneous mapping of distances to objects. Indeed, such an instantaneous determination would need the transmitted wave to have a very high power to reach an extensive area of the image, which is incompatible with the forming of portable devices.
The use of triangulation methods in which a laser scans a scene to obtain the distance to objects of this scene is also known. However, such methods are only accurate if the scene is not moving: they may need too long a response time to acquire information corresponding to a moving scene.
Thus, most known solutions require transceiver system which should be accurately aligned, an active light source, and/or imply long response times.